The present invention relates to an apparatus for driving an AC motor at variable speeds, and more particularly to an apparatus for driving an AC motor at variable speeds which controls primary resistance and/or leakage inductance of the AC motor at the desired values.
As seen in FIG. 13, a block diagram of a prior art variable-speed driving apparatus, an AC motor such as an induction motor or a synchronous motor is designated 101, a power converter such as an inverter is designated 102, and a reference AC voltage value generator is designated 103. The reference AC voltage value generator 103 generates unique reference frequency and amplitude values of AC voltage supplied to the AC motor 101 via the power converter 102. This variable-speed driving apparatus drives the AC motor at variable speeds by employing the power converter as a variable-voltage and variable-frequency power supply. In FIG. 13, symbols v.sub.1a *, v.sub.1b *, and v.sub.1c * designate reference primary voltage values of three phases (a phase, b phase and c phase) of the AC motor 101, and symbols v.sub.1a, v.sub.1b, and v.sub.1c designate detected primary phase voltage values.
In the prior art apparatus shown in FIG. 13, the reference frequency and amplitude values generated from the reference AC voltage value generator 103 must be manually adjusted for each individual AC motor in order to stably drive a given motor, since optimum reference frequency and amplitude values differ depending on primary resistance of the AC motor attributable to resistance of a stator, wiring resistance of the AC motor 101, and leakage inductance. This requirement for manual adjustment is very burdensome due to complexity of relationship between the primary resistance or the leakage inductance and adjustment factors.
It is an object of the present invention to provide an apparatus for stably driving an AC motor at variable speeds.
It is another object of the present invention to provide an apparatus for stably driving an AC motor at variable speeds which does not require manual adjustments for each individual AC motor.
It is yet another object of the present invention to provide an apparatus for stably driving an AC motor at variable speeds which electrically adjusts equivalent primary resistance and leakage inductance of the AC motor to desired values.